Kernel: Do not try to use return value of []=

pkg/front_end/lib/src/fasta/kernel/frontend_accessors.dart

Index: pkg/front_end/lib/src/fasta/kernel/frontend_accessors.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/frontend_accessors.dart b/pkg/front_end/lib/src/fasta/kernel/frontend_accessors.dart
index 86a44b09d0e3a4af9734e923a63970021d180828..1a805be3af3eac01683dbd25bb4cc0c7dec3e57e 100644
--- a/pkg/front_end/lib/src/fasta/kernel/frontend_accessors.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/frontend_accessors.dart
@@ -27,13 +27,13 @@ abstract class Accessor {
       {bool voidContext: false}) {
     if (voidContext) {
       return _finish(new ConditionalExpression(buildIsNull(_makeRead()),
-          _makeWrite(value, voidContext), new NullLiteral(), type));
+          _makeWrite(value, false), new NullLiteral(), type));

[ahe, 2017/02/01 14:02:38]

I think this hits more cases than you expect, so I'm not sure this is the right
fix.

Try running:

dart pkg/testing/bin/testing.dart --config=pkg/front_end/test/fasta/testing.json
compile

I think you'll see that you're changing some expectation files.

Do note that I haven't automated running these tests yet, and they're not up to
date, so you need to run the tests with and without your changes.

[kustermann, 2017/02/01 14:23:42]

The result of _makeWrite() is used, namely in a ConditionalExpression. So it
cannot be a void context. The VM will crash, because the _makeWrite() results in
caling []=() and the return value *is used*.

So why is this not a correct change?

There might be more such things, but I'm not claiming that I found all of them.
The same tests fail with and without this CL, namely:


12 failed:
compile/parser/parser_suite: Fail
compile/rasta/bad_constructor_redirection: Pass
compile/rasta/bad_explicit_super_constructor: Pass
compile/rasta/for_loop: Pass
compile/rasta/issue_000053: Pass
compile/rasta/issue_000068: Pass
compile/rasta/issue_000070: Pass
compile/rasta/malformed_function_type: Pass
compile/rasta/switch_execution_case_t02: Pass
compile/rasta/switch_fall_through: Pass
compile/rasta/try_label: Pass
compile/scanner/scanner_suite: Fail


Though it's quite difficult finding out if they fail the same way, because the
output of running this command is *huge*.

[ahe, 2017/02/01 14:33:16]

I was wrong. Thank's for clarifying.
Yes. I'm working on that right now.

     }
     var tmp = new VariableDeclaration.forValue(_makeRead());
     return _finish(makeLet(
         tmp,
         new ConditionalExpression(buildIsNull(new VariableGet(tmp)),
-            _makeWrite(value, voidContext), new VariableGet(tmp), type)));
+            _makeWrite(value, false), new VariableGet(tmp), type)));
   }
 
   Expression buildCompoundAssignment(Name binaryOperator, Expression value,